It is well known that turbocharged diesel engines yield a puff of smoke when accelerated rapidly from a low speed and/or low load condition. This results from the inability of the turbocharger to keep pace with the increase in fuel supplied during acceleration. The result is a temporary fuel-rich combustion which produces a "puff" of exhaust smoke.
Due to environmental concerns, particularly in recent times, various approaches have been made with various degrees of success to minimize this problem which otherwise, especially in vehicle applications, would cause turbocharged diesel engines to be objectionable. One of the approaches is based on the use of a pneumatic device that limits the fuel quantity to a low level whenever the air pressure in the intake manifold is low and allows for more fuel quantity (up to a preset fixed fuel schedule) as the pressure increases. Even though this approach is fairly simple and has produced some success in the control of acceleration smoke, it is rather restrictive on engine torque available during acceleration. The reason is that during acceleration the turbocharger has to speed up and develop a sufficient pressure before the device can start responding and allow for any increase in the fuel flow. Until such time, the engine torque is limited to a minimum. During acceleration the torque increase always lags behind the turbocharger, a characteristic inherent to pressure sensing puff limiting devices.